Display system where polarized light impinges on platelike laminate at brewster&#39;s angle or emerges therefrom at angle equal thereto

ABSTRACT

The invention relates to a display system where polarized light rays from a display device impinge on a laminate at Brewster&#39;s angle or emerge therefrom at an angle equal to Brewster&#39;s angle. This laminate is a combination of a transparent platelike object and a functional film that is an optical rotatory film or a semitransparent film. The platelike object has a front major surface, facing the display device, and a back major surface. The display device has a polarizing member for polarizing light rays of the display device into S-wave or P-wave light rays. According to a first embodiment of the invention, the optical rotatory film is formed on the front or back major surface of the platelike object or in an inside of the platelike object, and S-wave light rays from the polarizing member are thrown against the front major surface of the laminate. With this, a part of the S-wave light rays is reflected from the front major surface of the laminate toward a viewer. The rest of the S-wave light rays is transmitted in the platelike object and converted into P-wave light rays by the optical rotatory film. Then, substantially all of the P-wave light rays emerge from the back major surface of the laminate into the air at an angle substantially equal to Brewster&#39;s angle of the platelike object or the optical rotatory member, which borders on the back major surface of the laminate. Thus, the double image phenomenon does not arise.

BACKGROUND OF THE INVENTION

The present invention relates to a display system where polarized lightfrom a display impinges on a platelike laminate at Brewster's angle oremerges therefrom at an angle equal to Brewster's angle. This displaysystem can be used as a head-up display system which allows, forexample, the driver of a car to view vehicular information, whilelooking out a front windshield of the car, by projecting the vehicularinformation in the direction of the front windshield. Furthermore, thedisplay system of the present invention can be used for projectingvarious images, for example, on a shopwindow.

Hitherto, various head-up display systems have been proposed. Forexample, there is provided a head-up display system where a reflectionfilm, having a so-called half mirror property, is installed on thesurface of a single glass plate or in the inside of a laminated glass.In this head-up display system, light is inevitably reflected from theinboard or outboard surface of the glass plate, as well as from thereflection film. This causes a problem of double image (ghost)phenomenon. To eliminate this problem, for example, Japanese PatentFirst Publication JP-A-2-141720 discloses a head-up display systemhaving a phase film such as a λ/2 film. This film serves to rotate theplane of polarization of polarized light having a particular wavelengthof λ. JP-A-2-294615 discloses another head-up display system having atransparent birefringent film, for example, of polyethyleneterephthalate. U.S. Pat. No. 5,510,913, corresponding to JP-A-6-40271,discloses another display system having an optical rotatory filmcomprising a special liquid crystal polymer. JP-A-8-292393,corresponding to Japanese Patent Application 7-98878, discloses anautomotive head-up display system where a polarized S-wave impinges on alaminated glass. This laminated glass has inboard and outboard glassplates and an interlayer film disposed therebetween. Furthermore, anoptical rotatory film is disposed between the interlayer film and theinboard or outboard glass plate, and a semitransparent film is disposedon the inboard surface of the optical rotatory film. Still furthermore,a reflection preventive film is formed on the inboard glass plate.According to all of the above-mentioned publications, light from thedisplay device impinges on the glass plate at an angle that issubstantially equal to Brewster's angle.

SUMMARY OF THE INVENTION

The inventors assume that, according to all of the above-mentionedconventional publications, the light ray of the center line (opticalaxis) of the display device is designed to be incident on a transparentplatelike object (glass plate) at Brewster's angle, but the other lightrays except that of the center line are not. Therefore, we assume thatthe double image problem is not completely eliminated throughout theentire light rays from the display device in the above-mentionedconventional publications.

It is therefore an object of the present invention to provide a displaysystem where the double image problem is substantially completelyeliminated throughout the entire light rays of a display device.

According to the present invention, there is provided a display systemwhere polarized light rays from a display device impinge on a platelikelaminate at Brewster's angle or emerge therefrom at an angle equal toBrewster's angle, as will be clarified hereinafter. This platelikelaminate is a combination of a transparent platelike object and afunctional film that is an optical rotatory film or a semitransparentreflective film. The platelike object has front and back major surfacesopposed to each other. The display device has a polarizing member forpolarizing the light rays of the display device into S-wave or P-wavelight rays. The optical rotatory film of the platelike laminate rotatesa plane of polarization of light rays. In other words, the opticalrotatory film converts S-wave light rays into P-wave light rays, oralternatively converts P-wave light rays into S-wave light rays. Thesemitransparent reflective film of the platelike laminate reflects apart of light rays incident thereon and transmits the rest of the lightrays therethrough.

A display system according to a first aspect of the present invention ischaracterized as follows. The display device throws light rays that areintended to be viewed by a viewer, against a front major surface of theplatelike laminate, and its polarizing member polarizes the light raysinto S-wave light rays. Furthermore, the optical rotatory film is formedon the front or back major surface of the platelike object or in aninside of the platelike object. The platelike laminate has a back majorsurface that is an interface between the platelike laminate and an air.The front major surface of the platelike laminate faces the displaydevice such that a part of the S-wave light rays from the polarizingmember is reflected from the front major surface of the platelikelaminate towards the viewer and that the remainder of the S-wave lightrays is transmitted in the platelike laminate and is converted by theoptical rotatory film into P-wave light rays. The back major surface ofthe platelike laminate is curved such that substantially all of theP-wave light rays emerge from the back major surface of the platelikelaminate into the air at an angle that is substantially equal toBrewster's angle of one member of said optical rotatory film and saidplatelike object, which one member borders on the back major surface ofthe platelike laminate. In other words, when the optical rotatory filmis formed on the back major surface of the platelike object, the aboveangle is substantially equal to Brewster's angle of the optical rotatoryfilm. In contrast, when the optical rotatory film is formed on the frontmajor surface of the platelike object, the above angle is substantiallyequal to Brewster's angle of the platelike object. The above angle isdefined between a direction of propagation of the P-wave light ray inthe air and a line that is perpendicular to the back major surface ofthe platelike laminate at a point of emergence of the P-wave light rayfrom the platelike laminate into the air.

A display system according to a second aspect of the present inventionis characterized as follows. The optical rotatory film is formed on thefront or back major surface of the platelike object or in an inside ofthe platelike object. The display device throws light rays that areintended to be viewed by a viewer, against the front major surface ofthe platelike laminate, and its polarizing member polarizes the lightrays into P-wave light rays. The front major surface of the platelikelaminate is curved such that substantially all of the P-wave light raysfrom the polarizing member are incident on the front major surface ofthe platelike laminate at Brewster's angle.

A display system according to a third aspect of the present invention ischaracterized as follows. The display device throws light rays that areintended to be viewed by a viewer, against the front major surface ofthe platelike object, and its polarizing member polarizes the light raysinto P-wave light rays. The semitransparent film is formed on the backmajor surface of the platelike object. The front major surface of theplatelike object is curved such that substantially all of the P-wavelight rays from the polarizing member are incident on the front majorsurface at Brewster's angle of the platelike object.

A display system according to a fourth aspect of the present inventionis characterized as follows. The semitransparent reflective film isformed on the front major surface of the platelike object. The displaydevice throws light rays that are intended to be viewed by a viewer,against the reflective film, and its polarizing member polarizes thelight rays into P-wave light rays. The reflective film faces the displaydevice such that a part of the P-wave light rays from the polarizingmember is reflected from the reflective film towards the viewer and thatthe remainder of the P-wave light rays is transmitted in the reflectivefilm and then in the platelike object. The back major surface of theplatelike object is curved such that substantially all of the remainderof the P-wave light rays emerge from the back major surface thereof intothe air at an angle that is substantially equal to Brewster's angle ofthe platelike object. This angle is defined in the same manner as in thefirst aspect of the invention.

Thus, according to the present invention, the double image problem doesnot at all arise.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of a head-up display systemaccording to a first embodiment of the present invention;

FIGS. 2-4 are illustrations similar to FIG. 1, but respectively showingthose according to second to fourth embodiments of the presentinvention;

FIG. 5 is a diagrammatic fragmentary illustration of a head-up displaysystem according to the present invention, showing three tangents (S1,S2 and S3) at three points of a curved surface (not shown), on whichpolarized light rays from a display device (D) in directions along linesI1, I2 and I3 are incident at Brewster's angle (θ);

FIG. 6 is an illustration similar to FIG. 1, but showing another head-updisplay system according to the first embodiment;

FIG. 7 is an illustration similar to FIG. 2, but showing another head-updisplay system according to the second embodiment;

FIG. 8 is an illustration similar to FIG. 1, but showing still anotherhead-up display system according to the first embodiment; and

FIG. 9 is an illustration similar to FIG. 2, but showing still anotherhead-up display system according to the second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIGS. 1-9, a display system according to the presentinvention will be described in detail, as follows. As shown in FIGS. 1-4and 6-9, the display system has a platelike laminate, on which, forexample, the vehicular information is projected from a display device 2.This platelike laminate is a combination of a transparent platelikeobject 1 and the after-mentioned functional film formed thereon (seeFIGS. 1-4 and 6-7) or in an inside of the platelike object 1 (see FIGS.8-9). This transparent platelike object 1 may be a conventionalinorganic glass pane or an organic glass pane (e.g., resin plate), andit is not limited to a single plate. For example, it may be a laminatehaving a pair of transparent platelike objects and an interlayer filmsandwiched therebetween. Furthermore, it may be another laminate of aglass plate and a transparent resin plate, which is free of aninterlayer film therebetween (see FIGS. 8-9). A display system accordingto the present invention may be used as an automotive head-up displaysystem or an architectural display system.

According to the after-mentioned second and third embodiments of thepresent invention, as shown in FIGS. 2-3, 7 and 9, the transparentplatelike object 1 is curved to have a specially curved front (inboard)major surface such that all the polarized display light rays from thedisplay device are incident on the platelike laminate at Brewster'sangle of the platelike object or of the functional film. In contrast,according to the after-mentioned first and fourth embodiments of thepresent invention, as shown in FIGS. 1, 4, 6 and 8, a part of thepolarized light rays from the display device is reflected from thelaminate towards the eyepoint of the viewer, and the rest thereof istransmitted therethrough. Furthermore, the transparent platelike object1 is curved to have a specially curved back (outboard) major surfacesuch that the rest of the light rays, which has been transmittedtherethrough, emerges from the platelike laminate at an angle equal toBrewster's angle of the platelike object or of the functional film. Itshould be noted that the surface configuration of the functional film isin conformity with that of the platelike object, as illustrated. Thus,when the functional film is formed on the specially curved inboard oroutboard major surface of the platelike object, the functional film willalso have a specially curved surface in parallel therewith.

According to the after-mentioned first or second embodiment, an opticalrotatory film 3 is formed on an outboard or inboard specially curvedmajor surface of the transparent platelike object 1, or in an inside ofthe platelike object 1, thereby to constitute a laminate. Herein, theoutboard curved surface is defined as a surface from which the lightrays emerge (see FIG. 1), and the inboard curved surface is defined asthat on which the light rays impinge (see FIG. 2). The optical rotatoryfilm 3 may be a liquid crystal polymer film, a transparent birefringentfilm, or a λ/2 phase film.

According to the after-mentioned third or fourth embodiment, asemitransparent reflective film 4 is formed on the outboard or inboardcurved major surface of the transparent platelike object 1 to constitutea laminate. This reflective film 4 may be a metal thin film, forexample, made of Al, Ag, Au or Cu, or a metal oxide thin film, forexample, made of indium oxide or tin oxide.

In the invention, the display device 2 may be a cathodes ray tube (CRT),a fluorescent display tube, or a liquid crystal display. A polarizingmember 7 may be disposed between the display device 2 and the laminatesuch that a polarized S-wave or P-wave impinges on the laminate, as willbe clarified hereinafter. If desired, the polarizing member 7 may bebuilt in the display device 2 to constitute a single unit. If a liquidcrystal display (LCD) is used as the display device, the direction of apolarizing plate of the LCD may be designed such that light from thedisplay device is polarized into S-wave or P-wave. With this, it is notnecessary to provide an independent polarizing member.

According to the second and third embodiments shown in FIGS. 2-3, 7 and9, the transparent platelike object 1 is curved to have a speciallycurved major inboard surface such that all the display light rays areincident on the curved major inboard surface of the transparentplatelike object 1 or on the exposed surface of the optical rotatoryfilm 3 at Brewster's angle (θ) of the transparent platelike object 1 orthe optical rotatory film 3.

In the invention, it can be assumed that the eyepoint (E.P) of a viewerand a display device D are fixed at certain predetermined positionsshown in FIG. 5. In case that a display system of the invention is usedas an automotive head-up display system, the line of vision of theviewer for looking at the display light may be in slightly downwarddirections along lines R1, R2 and R3, in view of the displaymagnification and display quality of the display device D. The lines ofvision of the viewer along the lines R1 and R3 maybe respectively thosefor looking at the top and the bottom of the display image. The line R2may be a bisector of the lines R1 and R3. Thus, it becomes possible todraw a line I1 that intersects with the line R1 at an angle of 2 θ(i.e., twice Brewster's angle), from one end of the display device D, asillustrated. Similarly, it becomes possible to draw a line I2 thatintersects with the line R2 at an angle of 2 θ, from a middle point ofthe display device D, as illustrated. Furthermore, it becomes possibleto draw a line 13 that intersects with the line R3 at an angle of 2 θ,from the other end of the display device D, as illustrated. Then, itbecomes possible to draw a line segment S1 that is a normal to abisector of the lines I1 and R1, as illustrated. This line S1 is also atangent line of a reflective curved surface (not shown in FIG. 5) forreflecting the display light along the line I1 towards the eyepointalong the line R1. Similarly, it becomes possible to draw line segmentsS2 and S3 that are respectively a normal to a bisector of the lines I2and R2 and a normal to a bisector of the lines I3 and R3, asillustrated. These line segments S2 and S3 are also tangent lines of thereflective curved surface for reflecting the display lights along thelines I2 and I3 towards the eyepoint along the lines R2 and R3,respectively. This reflective curved surface (line) can substantially beformed by smoothly extending the line segments S1, S2 and S3 into anearly curved line segment. In other words, the transparent platelikeobject 1 is prepared so as to have a specially curved inboard and/oroutboard major surface that is identical with the above-mentionedreflective curved surface. In reality, a flat platelike object may beground or bent by a press to have a specially curved inboard and/oroutboard major surface. In fact, according to the second and thirdembodiments, the transparent platelike object 1 is prepared so as tohave a specially curved inboard major surface. Furthermore, the outboardmajor surface of the transparent platelike object 1 may be parallel withthe inboard major surface. To be accurate, according to the second andthird embodiments, the display light is reflected from the outboardsurface of the transparent platelike object 1. Therefore, it ispreferable to make a curve of the outboard surface, in view of thethickness of the platelike object. However, if the platelike object hasa thickness of up to about 2 mm, any practical problems do not arise bymaking the outboard surface of the transparent object 1 parallel withthe inboard surface. Similar to the second and third embodiments,according to the first and fourth embodiments, the transparent platelikeobject 1 is prepared so as to have a specially curved outboard majorsurface. Furthermore, the inboard major surface may be parallel with theoutboard major surface, as long as the platelike object has a thicknessof up to about 2 mm.

With reference to FIGS. 1, 6 and 8, a display system according to thefirst embodiment of the present invention will be described in detail,as follows. This display system as a head-up display system may bedisposed on dashboard of a car. The display system has a transparentplatelike object 1, for example, made of polymethyl methacrylate, havingthereon or therein an optical rotatory film 3, for example, made of aliquid crystal polymer. In fact, the optical rotatory film 3 may beformed on the inboard or outboard major surface of the platelike object1, as shown in FIGS. 1 and 6. Furthermore, as shown in FIG. 8, when theplatelike object 3 is a laminate of first and second plates, the opticalrotatory film 3 may be interposed between the first and second plates.Although not shown in FIG. 8, it is needless to say that the laminate ofFIG. 8 may have a conventional interlayer film for bonding the first andsecond plates together, besides the optical rotatory film. The displaysystem further has a display device (e.g., liquid crystal display) and apolarizing plate (not shown) for polarizing light from the displaydevice into S-wave. When the polarized S-wave is projected on thetransparent platelike object 1 (see FIGS. 1 and 8) or the opticalrotatory film 3 (see FIG. 6) at an angle substantially the same asBrewster's angle of one member of the platelike object 1 and the opticalrotatory film 3, which one member borders on the inboard major surfaceof the platelike laminate, part of the S-wave is reflected from theinboard major surface of the platelike laminate and then reaches theeyepoint of a viewer, as illustrated. In contrast, the rest of theS-wave is transmitted through the platelike laminate and is rotated intothe P-wave by the optical rotatory film 3, and then reaches an interfacebetween the outboard major surface of the platelike laminate and theair. It should be noted that the outboard major surface of the platelikeobject 1 is specially curved. With this, when the optical rotatory film3 is formed on the outboard major surface of the platelike object 1 asshown in FIG. 1, the exposed surface of the optical rotatory film 3 isalso specially curved in parallel with the outboard major surfacethereof Thus, substantially all of the P-wave light rays emerge from theoutboard major surface of the platelike laminate into the air at anangle θ that is substantially equal to Brewster's angle of one of theoptical rotatory film 3 and the platelike object 1, without reflectionfrom the interface towards the viewer. Thus, the double image phenomenondoes not arise. The angle θ is defined between a direction ofpropagation of the P-wave light ray in the air and a line that isperpendicular to the outboard major surface of the platelike laminate ata point of emergence of the P-wave light ray from the platelike laminateinto the air.

With reference to FIGS. 2, 7 and 9, a display system according to thesecond embodiment of the present invention will be described in detail,as follows. This display system has a transparent platelike object 1,for example, made of polymethyl methacrylate, having thereon or thereinan optical rotatory film 3 such as λ/2 phase film. In fact, as mentionedin the first embodiment, the optical rotatory film 3 may be formed onthe inboard or outboard major surface of the platelike object 1, asshown in FIGS. 2 and 7. Furthermore, as shown in FIG. 9, the opticalrotatory film 3 may be interposed between first and second plates of theplatelike object 1. Unlike the first embodiment, the display system hasa polarizing plate (not shown) for polarizing light from the displaydevice 2 into P-wave. When the polarized P-wave is projected on theinboard major surface of the platelike laminate at Brewster's angle ofone member of the optical rotatory film 3 or the platelike object 1,which one member bordering the inboard major surface of the platelikelaminate, all of the P-wave is transmitted into the platelike laminate,without reflection from the inboard major surface of the platelikelaminate. After that, the P-wave is rotated into S-wave by the opticalrotatory film 3, and then part of the S-wave emerges into the air fromthe outboard major surface of the platelike laminate. In contrast, therest of the S-wave is reflected from the outboard major surface of theplatelike laminate and then rotated by the optical rotatory film 3 intothe P-wave, and then reaches the inboard major surface of the platelikelaminate. Then, substantially all the light rays of the P-wave emergefrom the platelike laminate into the air and then reaches the eyepointof a viewer. Thus, the double image phenomenon does not arise.

With reference to FIG. 3, a display system according to the thirdembodiment of the present invention will be described in detail, asfollows. This display system has a transparent platelike object 1, forexample, made of polymethyl methacrylate, having thereon asemitransparent reflective film 4 such as an aluminum film. The displaysystem has a polarizing plate (not shown) for polarizing light from adisplay device 2 into P-wave. When the polarized P-wave is projected onthe inboard major surface of the transparent platelike object 1 atBrewster's angle of the platelike object 1, all of the P-wave istransmitted into the platelike object, without reflection therefrom.Then, part of the P-wave is reflected from the semitransparentreflective film, then transmitted in the platelike object 1, thenemerges from the inboard major surface of the platelike object 1, andthen reaches the eyepoint of a viewer. In contrast, the rest of theP-wave is not reflected from the reflective film 4, but is transmittedtherein and then emerges into the air. Thus, the double image phenomenondoes not arise.

With reference to FIG. 4, a display system according to the fourthembodiment of the present invention will be described in detail, asfollows. This display system has a transparent platelike object 1, forexample, made of polymethyl methacrylate, having thereon asemitransparent reflective film 4 such as an aluminum film, asillustrated. The display system has a polarizing plate (not shown) forpolarizing light from a display device 2 into P-wave. When the polarizedP-wave is projected on the inboard major surface of the reflective film4 at an angle substantially the same as Brewster's angle of thereflective film 4, part of the P-wave is reflected therefrom and thenreaches the eyepoint of a viewer. In contrast, the rest of the P-wave istransmitted in the reflective film 4 and then in the platelike object 1,and then reaches an interface between the outboard surface of theplatelike object 1 and the air. The outboard major surface of theplatelike object is specially curved such that substantially all of therest of the P-wave light rays emerge from the outboard major surfacethereof into the air at an angle θ that is substantially equal toBrewster's angle of the platelike object 1, without reflection from theinterface. Therefore, the double image phenomenon does not arise. Thisangle θ is defined in the same manner as in the above-mentioned firstembodiment.

The entire disclosure of Japanese Patent Application No. 9-174517 filedon Jun. 30, 1997, including specification, claims, drawings and summary,is incorporated herein by reference in its entirety.

What is claimed is:
 1. A display system comprising: a transparentplatelike object having a first and a second major surface opposed toeach other; an optical rotatory film for rotating a plane ofpolarization of light rays, said optical rotatory film being formed onsaid first or said second major surface of said platelike object or inan inside of said platelike object, a combination of said transparentplatelike object and said optical rotatory film constituting a platelikelaminate, said platelike laminate having a front major surface and aback major surface that is an interface between said platelike laminateand an air, and a display device for providing, against said front majorsurface of said platelike laminate, light rays that are intended to beviewed by a viewer, said display device having a polarizing member forpolarizing said light rays into S-wave light rays; and wherein saidfront major surface of said platelike laminate faces said display devicesuch that a part of said S-wave light rays from said polarizing memberis reflected from said front major surface of said platelike laminatetowards one-eye point of said viewer and that a remainder of said S-wavelight rays is transmitted in said platelike laminate and is converted bysaid optical rotatory film into P-wave light rays, wherein said backmajor surface of said platelike laminate is curved such thatsubstantially all of said P-wave light rays emerge from said back majorsurface of said platelike laminate into said air at an angle that issubstantially equal to Brewster's angle of one member selected from saidoptical rotatory film and said platelike object, said one memberbordering on said back major surface of said platelike laminate, saidangle being defined between a direction of propagation of said P-wavelight ray in said air and a line that is perpendicular to said backmajor surface of said platelike laminate at a point of emergence of saidP-wave light ray from said platelike laminate into said air.
 2. Adisplay system according to claim 1, wherein said platelike object has athickness of up to about 2 mm, and wherein said front major surface ofsaid platelike laminate is curved in parallel with said back majorsurface of said platelike laminate.
 3. A display system according toclaim 1, wherein said optical rotatory film is selected from the groupconsisting of a liquid crystal polymer film, a transparent birefringentfilm, and a λ/2 phase film.
 4. A display system according to claim 1,wherein said transparent platelike object is made of polymethylmethacrylate.
 5. A display system according to claim 1, which is anautomotive head-up display system.
 6. A display system according toclaim 1, wherein said display device is selected from the groupconsisting of a cathode-ray tube, a fluorescent display tube, and aliquid crystal display.
 7. A display system according to claim 1,wherein said platelike object is a laminate of first and second plates.8. A display system according to claim 7, wherein said optical rotatoryfilm is interposed between said first and second plates.
 9. A displaysystem according to claim 7, wherein said platelike object has aninterlayer film interposed between said first and second plates.